Shielding shoe for filters



y 10, 1956 N. G. LEFFLER 2,754,007

SHIELDING SHOE FOR FILTERS Filed July 16, 1951 2 Sheets-Sheet 1 I! Q 3JNI/ENTOR 1V1 ls Gusiay Lefifiler M, m #m ATTORNEYS y 10, 1956 N. G.LEFFLER snmnmc SHOE FOR FILTERS 2 Sheets-Sheet 2 Filed July 16, 1951[NVENTOR Nils Gusial/Leffler C d/221mm, Xflawum ATTURZVEYJ I E ha IUnited States Patent '0 SHlELDING SHOE FOR FILTERS Nils Gustav Lefller,Sundsvall, Sweden Application July 16, 1951, Serial No. 236,883

Claims priority, application Sweden August 14, 1945 13 Claims. (Cl.210201) The present invention relates to filters of the type embodying amovable perforated filter member adapted to pick up on its one sidesolids from a suspension and to discharge suspension liquid at its otherside after passage through the openings thereof under the influence of adifferential pressure. between said sides. Such a filter is usually, butnot always, formed as a rotary cylindrical drum the peripheral surfaceof which is perforated and provided with a fine mesh wire fabric forpicking up the solids of the suspension in which the drum is partiallysubmerged, and wherein the differential pressure is produced either byevacuating the interior of the drum or subjecting the outer surfacethereof to a superatmospheric pressure. The invention is especiallyadapted for embodiment in rotary drum filters for picking up solids,such as fibres, powders and granules, from suspensions in liquids and ismore particularly concerned with an improved construction of a shieldingshoe for such filters. application is a continuation-in-part of myprevious application Ser. No. 689,314, filed August 9, 1946, now PatentNo. 2,561,282, dated July 17, 1951, which was a further development ofthe invention I have disclosed in my application Ser. No. 652,464, filedMarch 6, 1946, now Patent No. 2,560,581, also dated July 17, 1951.

As in the case of my previous inventions above referred to, the presentinvention has also for its primary object to provide a shielding shoe ofthe kind defined which will secure a sufilciently good seading aroundthat portion of the wire fabric where the taking off takes place, andfurther to provide a shielding shoe which will close off the take offportion or zone effectively in filter drums even if the drum is notperfectly circular. An especial object of the present invention is toprovide a shielding shoe which will be more or less independent ofvariations in said difference in pressure.

The invention will now be described more in detail with reference to theaccompanying drawings illustrating various embodiments by which theinvention may be realized in connection with vacuum drums for papermaking but it is to be understood that the invention is not limited tothe features so shown but has to be taken in its broadest scope.

In the drawings:

Fig. 1 illustrates in cross sectional view the invention adopted in ashielding shoe comprising a movable band travelling with the filtermember,

Fig. 2 is a view of the shoe illustrated in Fig. I viewed from the righthand side, the filter member and part of the band being removed,

Fig. 3 is a cross sectional view of a portion of the filter drum at theupper roller of the shoe, taken along the line 3-3: in Fig. 1,

Fig. 4 is a fragmentary cross sectional view of a modified form of theshoe having plunger balancing means,

Fig. 5 is a cross sectional view, similar to that of Fig. 1, of ashielding shoe of the type illustrated in Fig. 5 of my Patent No.2,560,581 provided with pressure balancing means according to thepresent invention,

This I 2,754,007 Patented July 10, 1956 Fig. 6 is a view of the shoeillustrated in Fig. 5 viewed as Fig. 2, from the right hand side, thefilter member being removed and parts of the sealing portion of the shoebroken away and Fig. 7 is a fragmentary cross sectional view of anothermodified form of shielding shoe having a movable band like that of Figs.l-3 as well as plunger or piston balancing means of the characterillustrated in Fig. 4.

Referring first to Figs. 1 to 3, the filter drum comprises a cylindricperforated support or shell 1 on the outer surface of which the wiremesh fabric, not shown in the drawings, is applied for taking up thesolids suspended in a slurry of, for instance, cellulose fibres to formtherefrom the fibre cake 4. The support or filter member 1 is mounted inconventional manner in disc-like ends 2 being rotatably journalled inbearings, not shown in the drawings. At the outside of the filteringmember the doctor 3 is arranged in the usual way for removing the cake 4deposited on the filter. The drum is considered to rotate in thedirection of the arrow at the upper end of Fig. 1 and to be partlysubmerged in the fibre slurry 5. The interior of the drum may beevacuated in any of the ways well known to the art so as to maintain asubatmospheric pressure within the drum.

The shielding shoe is positioned at the place of discharge of thefilter, that is at the zone at which the fibre cake is removed from thedrum by the doctor knife and downwards to the level of the slurry 5. Thefunction of the shoe being to seal olf the communication between theinterior of the drum, the filtrate space or chamber 33, and the outeratmosphere, partly to facilitate the removal of the cake by shieldingolf the portion of the filter member at the removal zone from thepressure existing in the interior of the drum and partly to prevent airfrom getting access to the interior of the drum through the portion ofthe filter member made naked at the doctor, the shoe extends beyond thisplace of discharge at either side in the peripheral direction. The shoeis in the axial direction substantially coextensive with the filteringmember or with the foraminous portion thereof. In the drawings the shoeis submerged in the filtrate below the level 6 but this is not at allnecessary for its satisfactory function. In filter drums where thefiltrate is discharged at a low point in the drum the level of thefiltrate is preferably below the lowermost portion of the shoe.

In the embodiment shown in Figs. 1-3 the invention is applied to ashielding shoe comprising a rigid stationary shoe member 12 and amovable sealing shoe member in theform of an endless flexible band 7 ofrubber or steel or the like running over rollers 8 at either peripheralend of the. shoe, said band being tightened by means of a tighteningroller 9 suspended in an arm 10 and pressed by a spring 11, and beingadapted to contact and travelv with the perforated shell or screeningplate 1 along the portion thereof to be sealed at the taking off part ofthe drum. The screening drum being submerged in the fibre suspension 5,the vacuum prevailing in the interior of the drum will cause thesuspension liquid to penetrate the filter plate 1 so as to fill theinterior of the drum up to a givenlevel 6 determined by the continualremoval of filtrate liquid in conventional manner, not illustrated. Thefibre material deposits on the plate 1 forming a thin fibre cake 4successively increasing in thickness until the filter plate uponrotation of the drum will ultimately emerge from the suspension. 5 andcontinue its passage in the surrounding atmosphere where washing liquidorother treating liquid may be added over limited axial (longitudinal)sections of the drum and, due to the vacuum created in the interior ofthe drum, be sucked through the fibre cake. At least duringthe latterpart of the rotationof the drum in the atmosphere abovetthe fibresuspensiomairwill be sucked through the cake so that the latter is moreor less 3 dried. At the position near above the fibre suspension thefibre cake is ultimately removed from the screen by means of doctor 3.

The stationary shoe member 12 is securely mounted in the interior ofthedrum in conventional manner as on the shaft of the drum or on abracket attached to stationary end Walls of the drum, as the case maybe, not illustrated. The stationary shoe member 12 has a rigid centralwall 13 extending along the length of the drum and on a projectingportion 15 (best seen in Fig. 2), at each end of the stationary shoemember 12 a U-shaped fork piece 14 is pivoted by means of a shaft pin 16carrying the fork leg 21, extending by a portion 23 opposite shaft 16.The legs 21 and extension portions 23 are unitary, rigid parts of thefork piece 14. The projection 15 of the stationary shoe member 12projects into a recess 22 of the leg 21 and provides a stationarysupport for the axis of shaft 16. The roller 8 has a shaft 24 journalledin the portion 23 of leg 21. The fork 14 thus constitutes a pivotallymounted supporting means for roller 8 of the movable sealing shoemember, and the pivotal axis of shaft 16 on which said supporting meansis mounted is so located that certain portions of said means, i. e., thelegs 21 and extension portions 23 of fork 14, lie on one side of saidaxis while the cross bar or bottom portion of the fork lies on theopposite side. A spring 25 presses the roller towards the filter plate 1so as to render contact between band 7 and the plate. The cross bar orbottom portion of the fork 14 extends along the roller 8 and is insubstantially liquidtight contact therewith. The bar is sealed againstthe stationary central wall 13 by means of a sealing bar 17 fitted in agroove 18 in the fork 14. The bottom portion of the groove 18communicates with a pressure chamber 19, which lies between wall 13 andband 7, through a plurality of small channels formed in the fork,whereby the pressure in chamber 19 will press bar 17 against wall 13.Bar 17 may also be fitted in a groove in wall 13 similarly to theconstruction illustrated in Fig. 4.

The cross bars or bottom portions of forks 14 thus form closing membersfor the spaces between rollers 8 and wall 13 which would otherwiseprovide passages between the filtrate chamber 33 and the pressurechamber 19 which is sealed off or secluded from the rest of the filtratechamber by said wall, the rollers 8 and the forks 14. Each fork 14 alsoacts as a counterbalancing member for the associated roller 8 since, asis evident from Figs. 1 and 2, the roller 8 and the cross bar of fork 14lie on opposite sides of the axis of fork pivot shaft 16.

In this manner both of the rollers 8 are so mounted as to press with agiven power band 7 against the filter plate 1 at the ends of the shoe.The intermediate portion is pressed against the plate by means of apressure medium, preferably water, introduced at a preferably constantpressure into the pressure chamber 19 through pipe 26, which is passedthrough the end wall of the drum in any conventional manner. Thepressure chamber 19 is sealed against the filtrate chamber 33 of thedrum crosswise thereof by the rollers 8, the longitudinal cross bars offorks 14, the sealing bars 17 and the stationary central wall 13 as wellas the packings 27 sealing against the ends of the rollers. In the axialdirection of the drum the sealing is secured by means of side walls .ofthe stationary wall and sealing bars 28 engaging the filter plate 1 outside the perforations thereof. The bars 28 are suspended in cars 39 onwall 13 via links 29 and are pressed against the plate 1 by springs 31.The central and side walls of stationary shoe member 12, forks 14,rollers 8 and the associated sealing elements 17, 27 and 28 thus form anenclosure for pressure chamber 19, the open side of which faces and issubstantially coextensive in area with the portion of the filter member1 which it is desired to .seal off from the filtrate space 33, and isclosed by t e band 7.

By appropriately choosing the dimensions of the .surface. of the fork 14exposed to. the pressure chamber 19 in relation to the surface of roller8 facing the pressure chamber and the moment levers of these pressuresurfaces relative to the pivoting shaft 16 it is possible wholly orpartly to eliminate the effect of the difference between the pressuresin the filtrate chamber 33 and the pressure chamber 19, the latter beingaccommodated to and being dependent on the pressure outside the filterdrum, usually the atmospheric pressure. If the pressure surfaces andmoment levers are so chosen as to render the total pressures exerted onthose portions of said surfaces lying on opposite sides of the axis ofshaft 16 substantially equal, the fork and roller assembly will bebalanced and the pressure of roller 8 against band 7 will be dependentupon spring 25. By making the pressure surface of fork 14 or the momentlever thereof or both greater than those of the roller the influence ofthe fork will dominate over that of the roller causing the latterperpetually to be pressed towards the filter plate 1 by a pressuredependent on the pressure head in the pressure chamber 19 over that inthe filtrate chamber 33. In this case the spring 25 may, if desired, bedispensed with.

In Fig. 4 a modified structure is illustrated which may with advantagebe used in shoes having no travelling band. This embodiment is in manyrespects similar to that illustrated in Figs. 1 to 3 and thereforesubstantially only structural features different from those describedwill now be particularly described.

The central wall 13 of the stationary shoe member of Fig. 4 is providedwith a pair of piston devices (one at each end of the wall) eachcomprising an opening 40 in said wall, which may with advantage becylindric, and a pressure actuated plunger or piston 41 movable thereinand sealed against the wall of the opening by packing 42. The plungers41 thus form closing members for the passages provided by openings 40between the filtrate chamber 33 and chamber 19, and the latter issecluded from the rest of the filtrate chamber by wall 13, rollers 8 andplungers 41. Each plunger is secured to a rod 43 journalled in bearing44 and carrying at the end projecting into the filter chamber 33, apressure transmitting lever 45 by means of pin 46. Lever 45 is pivotallysupported on the stationary portion of the shoe, by means of a pin 47and has a projection 48 in which roller 8 is pivoted by means of shaft49, the projection being so arranged as to form with the body of arm 45a double armed lever pivoted about the stationary axis of pin 47 andconstituting supporting means for the movable sealing shoe memberrepresented by roller 8. The projection 48 is pressed by a spring 25 ina direction to cause roller 8 to engage the inner surface of theperforated shell or plate 1 of the filter drum with a certain pressure,while an inwardly directed force on lever 45 resulting from thedifferential pressure on'plunger 41 causes a corresponding movement ofroller 8 in an outward direction to force the roller against the innersurface of the drum. The roller 8 is sealed against the stationary wall13 by means of a sealing bar 17 housed in a groove 18 in the wall 13and, in cooperation with the wall 13 and the roller at the opposite endof said wall, shields off the portion of the drum shell at the Zonewhere the fibre cake is removed. The groove communicates with thepressure chamber 19 by channels 2.6 similarly to the embodiment of Figs.1-3 so that bar 17 is subjected to the pressure of chamber 19 andconsequently the pressure outside plate 1, as chamber 19 communicatesfreely with the exterior of the drum through the perforations ofplate 1. By adequately proportioning the surface-50 of roller 8 exposedto chamber 19 in relation to the surface of plunger 41 exposed tochamber 19 and the effective moment levers of these pressure surfacesrelative to the pivoting pin 47 i. e., the relative lengths of leverarms 45 and 48, the plunger may act as a counterbalancing member for theassociated roller and the engaging pressure of roiler 8 against filterplate 1 can be made wholly or partly independent of the var a ons in thedifferential pressure between the filtrate chamber 33 and the pressurechamber 19. If desired, the influence of the plunger can be made todominate so that the pressure head in chamber 19 will provide a positiveengaging pressure of roller 8 against plate 1. In this case spring 25may be dispensed with.

In Figs. 5 and 6 the invention is illustrated as embodied in a structureof the type illustrated in Fig. 5 of my earlier Patent No. 2,560,581.The filter drum represented by the foraminous cylindric plate 1 issubmerged in the fibre suspension 5 and the fibres are picked up on theplate as described above forming a fibre cake 4 which is removed bydoctor 3 at a place somewhat above the level of suspension 5. The nakedportion of plate 1 between doctor 3 and suspension 5 is sealed by theshielding shoe having a stationary shoe member 12 supported in theinterior of the drum. The stationary shoe member 12 has a rigid centralsupport plate or wall 60 on which a movable sealing shoe member orshield 61 is suspended in cars 62 by pivotally mounted supporting meanscomprising links or arms 63 secured by pins 76 to a shaft 64 journalledin the ears for rotation about a stationary axis and pins 65 journalledin the shield. At either end of the shield 61 springs 25 are providedbetween supports 66 in the shield and 67 adjustably mounted in thestationary plate 60 by means of bolt 68. These springs warrant a givenengagement pressure of shield 61 against the filter plate 1. The-shieldhas a recess 71 situated just opposite the place where the fibre cake 4is to be removed and a pipe 72 connected to air pipe 73 by a flexibleconduit 74 opens in this recess, these means being provided forsupplying pressure air below the cake to facilitate its removal.

An arm 75 is also secured to the shaft 64 by a pin 76 so that arm 75 andlinks 63 are rigidly connected to each other and form the equivalent ofa double-armed lever. The other end of arm 75 is rotatably secured tothe piston rod 77 of the piston 78, movable in the piston cylinder '79,which is tightened along the wall of the cylinder by a packing 80. Thepiston rod 77 is journalled in a bearing 81 in the bottom of cylinder79. The space within cylinder 79 constitutes a chamber which is sealedofi or secluded from the remainder of the filtrate space 33 by thesurrounding portion of plate 60, piston 78 and packing 80, the piston 78forming a closing member for the end of said chamber which wouldotherwise provide a passage between it and said filtrate space. Althoughcylinder 79 is illustrated as having a circular cross section this isnot essential but the shape may be different, such as rectangular. Thecylinder chamber communicates through a pipe 82 with any convenientsource of pressure medium, such as the surrounding atmosphere. The pipes73 and 82 extend outside the drum preferably through the trunnion of thedrum in a manner not shown but obvious to those skilled in the art.

When in operation of the drum a vacuum prevails in the interior 33thereof the atmospheric pressure has a tendency to press shield 61inwards against the pressure of springs 25 as the atmosphere has accessto a great portion of the outer surface of the shield through theperforations of the filter plate 1 whereas the inner surface of theshield is exposed to the vacuum inside the drum. On the other hand, incase pipe 82 leads to the atmosphere, atmospheric pressure prevails alsoin cylinder 79 and imparts to piston 78a tendency to move outwards ofthe cylinder, thus rotating arm 75 and link 63 secured thereto so as topress shield 61 outwards. By properly proportioning the surfaces ofshield 61 and piston 78 exposed to the differential pressure of theatmospheric pressure and the vacuum of the drum and the lengths of link63 and arm 75, the piston may act as a counterbalancing member for theshield and the pressure of the atmosphere over the pressure in theinterior of the drum can be balanced so that the influence of variationsin the vacuum in the drum upon the engagement pressureof shield 61 willbe reduced or eliminated. By increasing the surface of piston 78 or thelength of arm or both the influence of the piston may be dominating sothat a positive engagement pressure will be obtained by the influence ofthe pressure in cylinder 79. In this case springs 25 can be made weakeror be entirely dispensed with.

In addition to or supplementary to the balancing efle'ct obtained byadequately dimensioning the pressure surface of piston 78 and the lengthof arm 75 the present object can be obtained by using a medium forpiston cylinder 79 of superatmospheric pressure.

The modified structure illustrated in Fig. 7 is substantially the sameas that of Fig. 4 with the addition of an endless flexible band 7running over rollers 8 and a pipe 26 for supplying fluid under pressureto chamber 19, which added elements are counterparts of those bearing;the same reference characters in Figs. 1-3. The construction and mode ofoperation of the shielding shoe of Fig. 7 will be obvious from theforegoing description of the devices of Figs. 1-3 and 4.

As used in the foregoing specification and appendedt claims, the wordpressure will be understood to meant fluid pressure, except Where it isevident from the context: that mechanical pressure is intended.

I claim:

1. A shielding shoe for filters of the type embodying a movableperforated filter member adapted to pick up: on its one side solids froma suspension and to discharge: suspension liquid at its other side afterpassage through the openings thereof under the influence of adifferential pressure between said sides, said shoe being substantiallycoextensive with the width of the perforated portion of said filtermember and comprising a rigid stationary shoe member, supporting meanspivotally mounted on said stationary shoe member for movement about astationary axis so located that portions of said supporting means lie onopposite sides of said axis, a roller rotatably supported by saidsupporting means with the roller axis offset from said stationary axis,an endless flexible member of impervious material movable about saidroller and along with and in part in contact with said movable filtermember, said stationary shoe member including walls cooperating withsaid supporting means and said roller to form a chamber having an openside facing said movable filter member, means including the part of saidendless member in contact with said movable filter member for closingthe open side of said chamber and rendering the latter substantiallyliquidtight, and means for supplying a fluid under pressure to saidchamber, the surfaces of.said roller and said supporting means exposedto the pressure insaid chamber being so dimensioned and disposedrelative to the stationary pivotal axis of said supporting means as torender the total pressures exerted on those portions of said surfaceslying on opposite sides of said axis substantially equal.

2. A shielding shoe for filters of the type embodying a movableperforated filter member adapted to pick up on its one side solids froma suspension and to discharge suspension liquid at its other-side afterpassage through the openings thereof under the influence of adifferential pressure between said sides, said shoe being substantiallycoextensive with the width of the perforated portion of said filtermember and comprising a rigid stationary shoe member, supporting meanspivotally mounted on said stationary shoe member, a roller rotatablysupported by said supporting means, and an endless flexible memberofimpervious material movable about said roller and along with and inpart in contact with said movable filter member, said stationary shoemember being so constructed and arranged as to form in cooperation withsaid supporting means and said roller the walls of a chamber having anopening facing said movable filter member, means including the part ofsaid endless member in contact with said filter member for closing saidzms goo z opening and forming with said stationary shoe member asubstantially liquid tight chamber, said supporting means comprising aU-shaped member having two legs and a bottom portion, means forjournaling said roller in said legs, and means for pivotally connectingsaid legs to said stationary shoe member for movement about a stationaryaxis olfset from the axis of said roller.

3. A shielding shoe for filters of the type embodying a movableperforated filter member adapted to pick up onits one side solids fromasuspension and to discharge suspension liquid at its other side afterpassage through the openings thereof'uuder the influence of adifferential pressure between said sides, said shoe being substantiallycoextensive with the width of the perforated portion of said filtermember and comprising a rigid stationary shoe member, at least oneroller adapted to be supported on said stationary shoe member, anendless flexible member of impervious material movable about said rollerand along with and in part in contact with said movable filter member,said stationary shoe member being so constructed and arranged as to formin cooperation with said roller the walls of a chamber having an openingfacing said movable filter member, means including the part of saidendless member in contact with said filter member for closing saidopening and forming with said stationary shoe member a substantiallyliquid tight chamber, means for supplying a fluid under pressure to saidchamber, a lever at each end of said roller pivoted on said stationaryshoe member for movement about a stationary axis offset from the axis ofsaid roller, said roller being journaled in one arm of each of saidlevers, a pair of piston devices in said stationary member responsive tothe pressure in said chamber, and means connecting the pistons of saidpiston, devices to the other arms of said levers at points ofiset fromsaid stationary axis.

4. A filter for extracting fibres or the like in the form of a cake froma fibre pulp mixture, comprising a rotary drum adapted to be coveredover a portion of itscircumference by the pulp mixture and to maintainin its interior a pressure lower than that which prevails outside thedrum, said drumhaving a perforated shell, a shielding shoein theinterior of said drum including a sealing shoe member adjustable towardsand away from the inner surface of said perforated shell and cooperatingwith a portion of said inner surface of' said shell at a zone at whichthe fibre cake is removed from the outer face of said shell so as toshield otf said portion of the shellat said zone from the pressure inthe interior of said drum, said shielding shoe having a wall with. anopening therein, a pressure actuated member closing said opening. andcapable of movement relatively to said wall under the influence of thepressure difference betweenthe pressure exerted against the side of saidwall facing said drum and the pressure in the interior of said drum, anda pressure transmitting device supported in the interior of said drumand operatively connected to said pressure actuatedmember and to saidsealing shoe member in such manner that said device is causedto moveunder theinfiuence of an inwardly directed force resulting, from thedifferential pressure on said pressure actuated member and thereby tocause a corresponding movement of, said sealing shoe member intheoutward direction to force said sealing shoe member against the innerface of said drum.

5. A filter for extracting fibres or the like in the form of-a cake froma fibre pulp mixture, comprising a rotary drum adapted to be coveredover a portion of its circumference by thepulp mixture and to maintainin its inte-rior a pressure lower than that which prevails outsidethedrum, said drum having a perforated-shell, a shielding shoe in theinterior of saiddrum including a sealing shoe member adjustable towardsand away from the inner surface of'said perforated shell at a zone atwhich the fibrecake is removed from the outer 'faceof said shell so-astto shield oif said portion of the shell at-saidzone from the pressurein theinterior of said drum, said shielding shoe having a wall withanopening therein, a pressure actuated member closing; said opening andcapable of movement relatively tosaid wall under the influence of thepressure difference between the pressure exerted against the side ofsaid wall facing said drum and the pressure in the interior of saiddrum, and a pressure transmitting device comprising a double-armed leverpivotally supported in the interior of said drum for movement about astationary axis, means pivotally connecting one arm of said lever tosaid pressure actuated member, and means pivotally connecting the otherarm of said lever to said'sealing shoe member, whereby inward movementof said first mentioned arm of said lever under the action ofaninwarddirected force produced by the differential pressure on saidpressure actuated member results in outward movement of said lastmentioned arm of said lever producing an outward directed force actingupon said sealing shoe member.

6. A filter as claimedin claim 5 in which the areas of said pressureactuated member and said sealing shoe member subject to said pressuredifference are so related and said arms of said lever have such relativelengths that the product of, the area of said pressure actuated memberand thelength of the lever arm connected to said member is greater thanthe product of the area of said sealing shoe member and the length ofthe lever arm connected to said sealing shoe member.

7. A shielding shoe for filters of the type embodying a movableperforated filter member adapted to pick up on its one side solids froma suspension and to discharge suspension liquid at its other side afterpassage through the openings thereof under the influence of adifferential pressurebetween said sides, said shoe comprising a rigidstationary shoe member, supporting means pivotally mounted on saidstationary shoe memher, for movement, about a stationary axis, saidstationary hoemember including a central wall substantially coextensive. with the width of said filter member and side walls extendingin the direction of movement of said filter, member, asealing shoemember at at least one of the ends of'said' central wall movable towardsand away from said filter member, sealing means between said sealingshoe member'and said central wall, said sealing shoe member beingsupported by said supporting means, and means including said centralwall, side walls, supporting means, sealing meansand sealing shoe memberforming an enclosure having one side substantially co extensive with aportion of said filter member, said sealing shoe, member and saidsupporting means having surfaces lying on opposite sides of thestationary pivotal axis ofsaid' supporting means exposed to the pressurein said enclosure, said, surfaces being so dimensioned and disposedrelative to said axis as to render the total pressures exerted on thoseportions of said surfaces lying on opposite sides of. said axissubstantially equal.

8. A shielding shoe for'filters of the type embodying a movableperforated filter member adapted to pick up on its one side solids froma suspension and to discharge suspension liquid at" its other side afterpassage through the openings thereof under the influence of adifferential pressure between said sides, said shoe comprising a rigidstationary shoe member, supporting means pivotally mounted on saidstationary shoe member for movement about a stationary axis, saidstationary shoe member including a central wall substantiallycoextensive with the width of said'filtermember and side walls extendingin the direction of movement of said filter member, a sealingshoe memberat at least one of the ends of said central wall movabletowards and awayfrom said filter member, sealing means between said sealing shoe memberand said central wall, said sealing shoe member being supported bysaidsupporting means, and

means ineluding said central "wall, side walls, supporting means,sealing means and sealing shoe member forming an enclosure having oneside substantially coextensive with a portion of said filter member,said sealing shoe member and said supporting means having surfaces 1yingon opposite sides of the stationary pivotal axis of said supportingmeans exposed to the differential pres sure between the atmosphereoutside said walls and the pressure in said enclosure, said surfacesbeing so dimensioned and disposed relative to said axis as to render thetotal pressures exerted on those portions of said surfaces lying onopposite sides of said axis substantially equal.

9. A shielding shoe for filters of the type embodying a movableperforated filter member adapted to pick up on its one side solids froma suspension and to discharge suspension liquid at its other side afterpassage through the openings thereof under the influence of adifferential pressure between said sides, said shoe being substantiallycoextensive with the width of the perforated portion of said filtermember and comprising a rigid stationary shoe member, a lever pivoted onsaid stationary shoe member for movement about a stationary axis, asealing shoe member adapted to cover the portion of said filter memberto be sealed, said sealing shoe member being pivotally supported on onearm of said lever, a piston chamber in said stationary member, a pistonin said piston chamber responsive to the differential pressure betweensaid chamber and the atmosphere surrounding said stationary shoe member,and means connecting said piston to the other arm of said lever.

10. A shielding shoe for filters of the type embodying a movableperforated filter member adapted to pick up on its one side solids froma suspension and to discharge suspension liquid at its other side afterpassage through the openings thereof under the influence of adifferential pressure between said sides, said shoe comprising a rigidstationary shoe member, a lever pivoted on said stationary shoe memberfor movement about a stationary axis, said stationary shoe memberincluding a central wall substantially coextensive with the width ofsaid filter member and side walls extending in the direction of movementof said filter member, a sealing shoe member at at least one of the endsof said central wall movable towards and away from said filter member,sealing means between said sealing shoe member and said central wall,said sealing shoe member being pivotally secured to one arm of saidlever, said central wall, side walls, sealing means and sealing shoemember forming together with a portion of said filter member anenclosure, a piston device in said central wall responsive to thepressure in said enclosure, and means connecting the piston of saidpiston device to the other arm of said lever.

11. A shielding shoe for filters of the type embodying a movableperforated filter member adapted to pick up on its one side solids froma suspension and to discharge suspension liquid to a filtrate space atits other side after passage through the openings thereof under theinfluence of a differential pressure between said sides, said shoe beingsubstantially coextensive with the width of the perforated portion ofsaid filter member and comprising a rigid stationary shoe member,supporting means pivotally mounted on and sealed against said stationaryshoe member for movement about a stationary axis, a sealing shoe membermovable towards and away from said filter member, said sealing shoemember being supported by said supporting means, means for sealing off aportion of said filtrate space from the remainder thereof to form achamber wherein a different pressure prevails from that prevailing inthe remainder of said filtrate space, said sealing shoe member and saidsupporting means having surfaces against which said different pressuresare exerted and said surfaces being so disposed with respect to thepivotal axis of said supporting means that the differential pressureexerted on the surfaces of said supporting means tends to move saidsealing shoe member in a direction relative to said filter memberopposite to that in which said sealing shoe member tends to be moved bythe differential pressure exerted on the surfaces thereof.

12. A shielding shoe 'for filters of the type embodying a movableperforated filter member adapted to pick up on its one side solids froma suspension and to discharge the suspension liquid to a filtrate spaceat its other side after passage through the openings thereof under theinfluence of a differential pressure between said sides, said shoe beingsubstantially coextensive with the width of the perforated portion ofsaid filter member and comprising a rigid stationary shoe member,supporting means pivotally mounted on said stationary shoe member formovement about a stationary axis, a sealing shoe member movable towardsand away from said filter member, a wall formed at least in part by saidsealing shoe member for sealing off a portion of said filter member fromsaid filtrate space and separating said filtrate space from anotherspace wherein a different pressure prevails from that prevailing in saidfiltrate space, said sealing shoe member having one of its sides exposedto said filtrate space and its opposite side exposed to said otherspace, means in said filtrate space enclosing a space secluded from therest of said filtrate space and providing a passage between saidfiltrate space and said secluded space, the pressure prevailing in saidsecluded space being the same as that prevailing in said other space,and a closing member sealed aaginst said stationary shoe member andmovable relative thereto in said passage under the influence of thedifferential pressure between said filtrate space and said secludedspace, said closing member and said sealing shoe member being supportedby said supporting means in such mutual relationship to the stationarypivotal axis of said supporting means that the rotary movement of saidsupporting means induced by the movement of said closing member in saidpassage in a direction from said filtrate space towards said secludedspace is opposite to the rotary movement of said supporting meansinduced by the movement of said sealing shoe member in the directiontowards said filter member.

13. A shielding shoe for filters of the type embodying a movableperforated filter member adapted to pick up on its one side solids froma suspension and to discharge the suspension liquid to a filtrate spaceat its other side after passage through the openings thereof under theinfluence of a differential pressure between said sides, said shoe beingsubstantially coextensive with the width of the perforated portion ofsaid filter member and comprising a rigid stationary shoe member, asealing shoe member having one surface exposed to the pressureprevailing in said filtrate space and a second surface exposed to adifferent pressure, means for supporting said sealing shoe member onsaid stationary shoe member for movement towards and away from saidfilter member, said supporting means being pivotally mounted on saidstationary shoe member for movement about a stationary axis, and acounterbalancing member movable relative to and sealed against saidstationary shoe member and having one surface exposed to the pressureprevailing in said filtrate space and a second surface exposed to thesame pressure as that to which the second surface of said sealing shoemember is exposed, said sealing shoe member, supporting means andcounterbalancing member being so interconnected and disposed withrespect to the stationary pivotal axis of said supporting means that thedifferential pressures exerted on said sealing shoe member and saidcounterbalancing member tend to move said supporting means in oppositedirections about said pivotal axis.

(References on following page) References Cited in the file of thispatent UNITED STATES PATENTS Elling May 10, 1921 Berry May 10,. 1927Haug Mar. 8, 1932 Hillel et a1. Sept. 8, 1936 Cuno et a]; Apr. 20, I937Euahs May 19, 1942 12 Street July 21, 1942 Vitalius et' ali Dec. 19,1950 Lefiier- July- 17, 1951 Leffier July 17, 1951 FOREIGN PATENTSGermany Nov. 3, 1921 Great Britain Dec. 24', 1931

